1. Field of the Invention
This invention relates to a method for fabrication of an electrochromic (EC) device, and to an electrochromic device fabricated by such method. More particularly, the present invention is concerned with a method for fabrication of an electrochromic (EC) device using a gel-like electrolytic solution as the electrolyte, and also with such electrochromic device manufactured by that method.
2. Description of Prior Art
For the electrolytic solution of electrochromic (EC) devices, there has so far been used mostly a solution-type electrolyte using, for example, propylene carbonate, etc. as the solvent, and lithium iodide (LiI), a mixture of lithium perchlorate and ferrocene, and so forth as the electrolytic substance. However, solution-type electrolytes had various disadvantages such that, when the substrate for the electrochromic device is broken, the electrolytic solution contained therein scatters over the surrounding area, or, when the substrates are pressed from outside, the opposite electrode formed on the inner surface of each of the substrates comes into mutual contact to cause short-circuit, or various other troubles and disorders. Further, as the method for fabrication of electrochromic devices using the solution-type electrolyte, there has usually been adopted such one, in which an injection port is perforated in one of the two substrates having a layer of an electrochromic substance formed on the surface side of at least one of the substrates where electrode is provided; then, after formation of a cell by opposing these two substrates with their surface sides where the electrode is provided facing each other, and sealing the circumference of these substrates with a sealing material (or, after formation of a cell by perforating in advance the injection port in the sealed part), the electrolytic solution is injected into the cell through the injection port; and finally the above-mentioned injection port is closed. This method, however, also possessed various disadvantages such that bubbles tend to remain easily in the cell; the electrolytic solution tends to overflow readily from the above-mentioned injection port; and the thus overflown electrolytic solution has to be removed and washed after closure of the injection port.
On account of this, studies and research have been continuously undertaken in recent years for an improved electrochromic device free from the above-mentione disadvantages, in which use is made of a gel-like electrolytic solution obtained by adding an appropriate gelling agent to the afore-mentioned solution-type electrolyte. However, even in this method of fabricating the electrochromic device using such gel-like electrolytic solution, there has still remained a problem as to how the electrolytic solution can be introduced into a space between a pair of substrates. In more detail, since the electrolytic solution is in gel-form, it is difficult to inject such gel-like electrolytic solution by way of the injection port into the above-mentioned cell after it is formed. On account of this, a method has so far been contemplated, by which the gel-like electrolytic solution is heated to lower its viscosity which enables it to be injected into the cell of the electrochromic device through the injection port, after which the electrolytic solution is cooled to increase its viscosity again. This method, however, was poor in its working efficiency. It had such disadvantages that it took a long time for the injection of the electrolytic solution to fill up the cell, and therefore was not suited for mass-production in an industrialized scale. Moreover, there has also been contemplated a method, according to which, prior to formation of the cell by applying the sealing material on and around the circumference of the substrates, the gel-like electrolytic solution is held between the two substrates; then this electrolytic solution is pressed between the substrates, followed by scrapping of the electrolytic solution which is forced out of the substrates as the result of the pressing, and cleaning of the peripheral area of the substrates; and finally the substrates with their peripheral area having been cleaned are sealed with the sealing material to form the cell for the electrochromic device. This method, however, was still not suited for industrialized mass-production, because the electrolytic solution to be forced outside is not uniform in pattern, which makes it difficult to carry out the scraping work efficiently. In addition, the surrounding seal for the cell is rendered imperfect by the scraping work with the result that durability of the cell would become insufficient.
With a view to solving these points of problem, the present inventors have already proposed a method for fabricating the electrochromic devices, which comprises: forming, with use of a sealing material, cured inner banks constituting the external frame and uncured outer banks on the surrounding positions over the surface of a pair of substrates at their surface side where the electrode is provided; placing a gel-like electrolytic solution on the surface of the substrate; and contact-bonding the substrates to join them together.
However, even this method for fabrication of electrochromic devices had its own problem in production efficiency, because of precise controls having been required of the space interval, height, contact-bonding conditions, etc. for both inner and outer banks. In addition, there was a possibility of the uncured sealing material to constitute the outer banks getting over the inner banks at the time of the contact-bonding to come into contact with the electrolyte, thereby giving mal-effect to the electrolyte. Furthermore, as this sealing material becomes cured, stress from deformation is imparted to the substrates by the inner banks which have already been cured and the outer banks which will have become cured after the former with the consequence that the optical distortion is brought about, which was liable to form double images in case the thus fabricated electrochromic device is used as a light-control mirror, or the like.